Ultra high frequency ignition



o@ @a 1946- F. x. RETTENMEYER 2,408,881

ULTRA HIGH FREQUENCY IGNITION SYSTEM Filed May 29, '1942 m a m 1 nventor M egel',

(Iftome Patented Oct. 8, 1946 OFFICE ULTRA HIGH FREQUENCY IGNITION SYSTElfI v Francis X. Rettenmeyer, Moorestown, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application May 29, 1942, Serial No. 445,046

20 Claims. l

This invention relates generally to ignition systems for internal combustion engines and particularly to ignition systems utilizing voltages of ultra high frequency suitably coupled to sparking devices comprising resonant circuits including the spark gaps.

Present ignition 'systems for aircraft use have the distinct disadvantage that considerable radio interference is generated by the high potentials and comparatively low frequencies involved. Numerous ignition shielding devices are known for decreasing the inherent radio interference in such systems, but such devices have limited utility due to wide variations in moisture, pressure, and temperature gradients encountered in aircraft work. For example, when an airplane flies through a cloud, considerable condensation may occur within the shielding surrounding the high tension spark plug leads, resulting in reduced eilciency of the ignition system. Moreover at low pressures spark-over may occur. Various methods, including the use of air pumps, have been devised for exhausting the moisture, or increasing the air pressure, within the high tension electrostatic shielding, but the additional apparatus required adds weight and has other serious disadvantages.

The instant system utilizes the advantages of low inherent radiation from low impedance ultra high frequency transmission lines and, in addition, provides a simple and eflicient means, for removing continuously the moisture which accumulates within the outer shield of the transmission line. Ey utilizing ignition voltages of ultra-high frequency which are considerably above the normal frequencies used for radio transmission, and by transmitting the ignition voltages over low impedance transmission lines connecting an ultra high frequency generator to the individual spark plugs of the internal combustion engine, radio interference is reduced to a practical operating level.

Various methods and apparatus well known in the art may be utilized for generating the ultra high frequency potentials required for satisfactory ignition. It should be understood that the apparatus described herein is merely typical of the type of equipment which will provide satisfactory operation, and that the invention is not limited t0 the specific apparatus disclosed.

Among the objects of the invention are to provide a new and improved method of and apparatus for ultra high frequency ignition in internal combustion engines. Another object of the invention is to provide a new and improved method of and apparatus for generating the required potentials at ultra high frequency, transmitting these potentials over a low impedance transmission line, and applying the ultra high frequency potentials to a resonant circuit including a spark gap which is located within the combustion chamber of the internal combustion engine. A further object of the invention is to provide an improved method of and means for pulsing the output of an ultra high frequency oscillator to provide extremely high instantaneous power output with equipment of low continuous power rating. Another object of the invention i's to provide an improved method of and means for coupling successively high potentials of ultra high frequency to spark gaps within combustion chambers by means of individual low impedance coaxial cables suitably coupled to the equivalent of any odd multiple of quarter-wave resonant devices, each including a spark gap. .Another object is to provide a new and improved spark plug. A further object is to provide an improved and 'simplified means for removing moisture accumulations within the ignition transmission lines.

The invention will be described by reference to the drawing of which Figure 1 is a schematic circuit diagram of one embodiment of the invention: Figure 2 is an elevational view of an improved low impedance transmission line showing louvres for exhausting moisture accumulations, and Figure 3 is a cros-s-sectional view of Figure 2. Similar reference numerals are app-lied to similar elements throughout the drawing.

Referring to Fig. l., a power genera-ting source l which may be a suitable D.C. generator driven by the internal combustion engine is connected to a voltage divider 2, which is grounded at some intermediate point. If extremely high. anode voltages are required, an A.C. generator and transformer may be substituted for the 13.--C. power supply and voltage divider. Potentials de", rived from the voltage divider 2 are applied to the electrodes of an ultra high frequency oscillator tube 3 which includes an ultra high irc quency oscillator circuit comprising a predetern mined section of coaxial cable 4. However, the oscillator circuit may be of any other type known in the art. At extremely high frequencies, a magnetron circuit provides satisfactory power output. Pulsing of the oscillations generate-d in the thermionic tube circuit is accomplished by means of a suitable commutator device 5 connected in series with the vacuum tube anode power lead connected to the voltage divider 2. In practice, the pulsing commutator may be driven by the interna1 combustion engine, and synchronized with the engine cylinder ring. High potentials of ultra. high frequency, derived by suitable coupling to the oscillatory circuit 4, are applied to the rotating element 8 of a contact or capacity type distributor which may be also driven by the internal combustion engine and the switching rate of which is synchronized with the switching of the pulsing commutator device 5 described heretofore. The stationary elements l and 'l' of the distributor are connectedihrough a plurality of individual low impedance transmission lines 8 and B which may be conventional coaxial cable, to a plurality of special spark plug devices 9 and 9'. The spark plug have a length which is the equivalent or any cdd multiples of quarter-wave linesl which terminate in the spark gaps I and I0. The ends of the outer conductors 9, 9 of the plugs remote from the spark gaps. Il), l0', respectively, are short-cir cuited to the respective inner conductors ll, Il to provide voltage maxima at the spark due to standing waves thereby provided in the plugs. The short-circuited conductors are preferably entirely closed to provide a gas seal. It should he understood that wave guides may be used as transmission lines, and that they may be coupled to the distributor and spark plugs in any well known manner. The connection from the low impedance transmission line 8 passes through. the gas tight gasket I3 to the quarter-wave line ll, and should preferably be made at a point on the line II to obtain maximum power transfer when a spark occurs at the spark gap lll. The gasket I3 may be either conductive or insulation, dem pending upon whether .it is located at a voltage node, or at some other point. It should be unn derstood that the mechanical construction of the quarter\vave spark plug is not a limiting factor of this invention and that any arrangement other than that shown which provides the equivalent of an odd multiple of a quarter-wave load circuit will be equally satisfactory. The plug construction should preferably be adapted to he readily demountable from the cylinder head may include the conventional yscrew type spark plug supporting means.

The pulsing of the oscillator output by the pulsing commutator will provide an oscillator output of extremely high instantaneous power characteristics from an oscillator tube of low continuous power rating. Any other well known pulsing means, which may be suitably synchronized, would be equally satisfactory. As explained heretofore, the -low impedance transmisn sion line 8 will provide minimum radiation. The entire generator system including the oscillator, the resonant circuit, the pulsing commutator, the distributor and the power generator should preierably be enclosed within an electrostatic shield i2. The sheaths 8 and 8' of the low impedance transmission line should preferably be gounded to the electrostatic shield and to the common ground of the internal combustion engine.

Referring to Fig. 2, a modication of the low impedance transmission cable includes an inner conductor 52 connected at a suitable point to the quarter-wave transmission line l l comprising a spark plug. The outer concentric sheath includes a plurality of louvres 53 having openings 54. If a column of air is directed coaxially along the transmission line in the direction indicated by the arrow, low pressure areas will occur in the vicinity of each of the openings 54, providing satisfactory exhaustion of the moisture Within the transmission cable. The openings 54 may be arranged at desired intervals around the sheath 5| or, if desired, may be limited to the lower surfaces thereof. Fig. 3 illustrates more clearly the louvre formation.

The term transmission line as used in t-he appended claims is intended to include all known types of lines, such as for example, coaxial lines, balanced lines, single and multi-conductor lines, and Wave guides. Any suitable known means may be provided for coupling the spark gaps and the distributor to the particular type of transmission line utilized.

I claim as my invention:

1. An ignition system including a source of ultra-high frequency oscillations, means for pulsing said oscillations, at least one spark gap device comprising a resonant line including one of said gaps and upon which standing waves may be established at said ultra high frequency, and means including separate low impedance transmission lines alternately connecting said source to each of said spark gap devices at a point intermediate a voltage node and voltage loop of said standing waves on said resonant line.

2. An ignition system including a source of ultra-high frequency oscillations, means ior pulsing said oscillations, at least one spark gap device comprising an odd multiple of a quarterwave line including one ci said gaps, and means including separate low impedance `transmission lines successively connecting said source to each of said spark gaps.

3. An ignition system including a source of ultra-high frequency oscillations, means for pulsing said oscillations, a plurality of spark gap devices each comprising an odd multiple of quarterwave lines including one oi said gaps, low impedance transmission lines connected to each of said devices, and switching means for selectively connecting said source to each of said low impedance transmission lines.

4. Apparatus of ,the type described in claim 3 including means for synchronizing the operation f of said pulsing means and said switching means.

5. Apparatus of the type described in cla-im 3 characterized by the fact that the frequency o said oscillations is in excess of 500 megacycles.

6. Apparatus of the type described in claim 3 characterized by the fact that said source of oscillations includes a thermionic tube and a section of coaxial cable of predetermined dimensions,

7. An ignition system for an internal combustion engine including power generating means, ultra-high frequency generating means including a thermionic tube and a resonant section of coaxial cable, pulsing means, means including said pulsing means for connecting said power generating means to said ultra-high frequency generat ing means, a plurality of spark gap devices each comprising an odd multiple oi quarter wave lines including one of said gaps, low impedance trans-- mission lines connected to each of said devices, switching means for connecting selectively said ultra-high frequency generating means to each of said low impedance lines, and means for synchronizing the opera-tion of said pulsing means and said switching means.

8. Apparatus of the type described in claim 'l characterized by the fact that said ultrahigh frequency is in excess of 500 megacycles.

9. Apparatus of the 4type described in claim 7 including grounded electrostatic shielding means enclosing said system.

10. Apparatus of the type described in claim 3 including grounded electrostatic shielding means enclosing said system.

11. In an ultra-high frequency ignition system for internal combustion engines including a plurality of spark gap devices each comprising an odd multiple of quarter Wave lines including said gaps, the method including generating oscillations in excess of 500 megacycles, pulsing said oscillations, switching said pulsed oscillations, successively transmitting said switched oscillations at low potential to each of said spark gap devices and successively applying said low potential oscillations to each of said devices at a point intermediate a voltage loop and a voltage node of said quarter wave line- 12. In an ultra Ihigh frequency ignition system including an ultra high frequency generator, a plurality of sparking devices and individual low impedance coaxial lines connecting said generator `to said sparking devices, spaced apertures in said coaxial lines, air deflecting means in operable relation to said apertures, and means including said deflecting means for varying the air pressure within said coaxial lines.

13. A tuned Spark plug for ultra-high frequency ignition voltages including an elongated center electrode, a -coaxially disposed :cylindrical electrode surrounding said center electrode, means connecting one end of said center electrode to the proximate end of said cylindrical electrode, means forming a Spark gap between the remaining ends of said electrodes, and .connecting means for said ultra-high frequency voltages intermediate the ends of said center electrode and to said cylindrical electrode.

14. A tuned spark plug for ultra-high frequency ignition voltages including an elongated center electrode of length equivalent to some odd multiple of one quarter wavelength of said voltages.

1'5. Apparatus of the type described in claim 13 including means for connection to a transmission line, characterized by .the fact that said yconnecting means is connected to said center electrode at a point providing effective impedance matching between said transmission line and said spark gap.

16. Apparatus of the type described in claim 14 including means for connection to a transmission line, 4characterized by the fact that said connecting means is connected to said center electrode at a point providing effective impedance matching between said transmission line and said spark gap.

17. Apparatus of the type described in claim 13 including threaded mounting means for supporting said cylindrical electrode.

18. An ignition system including a source of ultra-high frequency oscillations, a plurality of ignition devices each comprising a resonant structure upon which standing Waves may be established at said ultra-high frequency to raise substan-tially the temperature at a predetermined point in said device, :and means -including separate low impedance transmission lines connecting said source to each of said ignition devices.

19. An ignition system including a source of ultra-high frequency oscillations, means for pulsing said oscillations, at least one ignition device comprising a resonant structure upon which standing waves may be established at said ultrahigh frequency to raise substantially the temperature at a predetermined point in said device, and means including separate loW impedance transmission lines connecting said source to each of said devices.

20. A resonant ignition plug for ultra-high frequency voltages including an elongated cen-ter electrode of length equivalent to some odd multiple of one-quarter Wavelength of said voltages.

FRANCIS X. RETTENMEYER. 

